The present invention relates generally to the field of digital image sensors.
Digital image sensors are used in a wide variety of applications. In some applications, images produced by these sensors are used to make critical decisions, such as in medical imaging applications where accurate image renditions can be crucial to the process of making diagnoses. The image sensors are typically composed of millions of photo-sensitive cells or pixels which transform light received into the cells into voltage output. The conversion of light to electrical signals is determined by a transfer characteristic, and each cell typically has its own transfer characteristic. The output of the image sensor, therefore, are a series of electrical pulses, each of which represents the reading of an individual cell. A processor receives the electrical pulses and converts the data into a digital representation of the image, which is then stored on a disk from which it can be displayed, archived, or printed out on a printer.
Due to manufacturing defects, a new image sensor plate may have many individual pixels malfunction, and occasionally may even have an entire column malfunction which contains thousands of pixels. However, even with these defects, a sensor plate can still record an accurate, smooth, representation of a subject. This is accomplished by interpolating the data for the malfunctioning pixels from the surrounding functioning pixels. Although this technique is effective, critical information may be lost if the interpolation process is applied to a large number of pixels or a group of pixels in a cluster. For example, in a medical application, the interpolated data may obscure actual data critical to an accurate diagnosis.
A recurring problem in the use of conventional image sensors is the re-configuration of the computer system that is required each time a new image sensor is installed. In order to interpolate around the defective pixels, the computer system must be able to access the defect information for a plate. Thus, each time a plate is removed, a technician must install the defect map for the replacement plate into the computer system. Installing the defect map is time-consuming, burdensome, and leads to erroneous images if not properly completed at the time when the replacement image sensor plate is installed. Additionally, when a pixel becomes defective after leaving the manufacturing site, the only method to detect a malfunction is to manually calibrate the plate. Manual calibration is also a burdensome, error-prone process which increases the overall cost of using an image sensor plate. Therefore, there is needed an image-sensing device that is capable of being replaced without having to update an associated computer system, which is able to detect whether a pixel located within the sensor plate has become defective or whether an increasing number of pixels are failing, and respond accordingly. Additionally, there is a need for a plate which can alert a user to discontinue use of the sensor when the number or configuration of malfunction pixels indicates that the interpolation process is no longer appropriate.
In a preferred embodiment, a self-diagnosing image sensor (100) stores maps of functioning and malfunctioning pixels (124) or clusters of such pixels in a memory (144) directly coupled to the image sensor (100). The memory (144) is coupled to an external monitoring computer (118) which retrieves the pixel map and adjusts the sensor data received from the image sensor (100) in accordance with the retrieved pixel map. In a further embodiment, a defect discriminator (140) is coupled directly to the image sensor (100) and the memory (144), detects whether a pixel (124) malfunctions, and updates the map accordingly. In this embodiment, multiple versions of the map generated at different times are stored in the memory (144) to provide a diagnostic history of the plate (100). Additionally, if the number of malfunctioning pixels (124) in the map exceeds a predefined threshold, an alert message is transmitted to the external monitoring computer or display (118) to warn the user that the sensor (100) may be generating inaccurate information. Alternatively, the image sensor (100) compares a newly generated map with a previous version of the map. If there are any changes, the user is notified. The external monitoring computer (118) may also request status information regarding the pixels from the image sensor (100) at any time. Finally, an on-plate pixel processor (148) is coupled to the memory (144) to generate interpolated data. In this embodiment, the external monitoring computer (118) need only display the interpolated image; no further processing is required outside of the plate (100).